THIS INVENTION relates to extracting a pick holder from a pick box in a continuous miner drum; to extraction means for carrying out the method of the invention, to a pick holder, and to an extraction tool.
In one kind of continuous miner, for example a continuous miner manufactured by the firm Voest Alpine, there is provided a plurality of pick boxes arranged in predetermined fashion on a drum of the continuous miner. Each pick box has a substantially blind socket within which a pick holder is replaceably received. A shank of a pick is in turn replaceably received within the pick holder such as to allow rotation of the pick relative to the pick holder in use. Receipt of the pick holder in the pick box is by means of a tight, frictional, press fit. The pick holder is to be removable to allow replacement, reconditioning, and the like.
In known pick holders there is provided an internal circumferential groove to retain a pick in use via a retaining ring on a shank of the pick. One way to remove the pick holder from the pick box (when the pick has been removed), is by dilating a collar on a shank of an extracting tool to locate in said internal circumferential groove and to apply an extraction force on the shank. The force is then transmitted via a shoulder of the internal circumferential groove to extract the pick holder from the pick box.
Although this method is generally used, it has at least two problems. First, the integrity of locating the collar of the extracting tool in the internal circumferential groove is not good. It does happen that the internal collar slips, which may result in a very unsatisfactory and possibly dangerous situation and possible damage to equipment. Second, the collar of the extracting tool is to be dilatable to enable it to engage the internal circumferential groove, thus requiring a composite (more than one part) design which is expensive to manufacture. Such extracting tool becomes worn fairly quickly and has to be reconditioned or replaced after a relatively small number of extracting operations.
An alternative, known, method is to provide an external circumferential groove in a portion of the outer surface of the pick holder which protrudes from the pick box. This method has generally the same disadvantages as the first mentioned known method. In addition, the external circumferential groove is exposed to the working conditions and becomes worn and unusable for locating purposes fairly quickly. Furthermore , the protruding portion or head may shear of f, which renders extraction by means of the external groove impossible.
It is an object of this invention to provide a method, an extracting means, a pick holder and an extraction tool which improve on the prior art and which do not suffer, or at least suffer to a smaller degree, from the problems of the prior art.